This invention relates to an apparatus for forming a desired pattern on a plate-like object with a beam of electrons or ions, and more particularly to such a pattern forming apparatus which is useful in engraving a desired electric circuit pattern on the properly treated major surface of a semiconductor substrate.
In fabricating integrated circuits and other precision semiconductor devices, the photolithography technique has hitherto been used. But disadvantageously, the accuracy with which a desired pattern can be formed on a substrate is limited by the diffraction effect which depends on the wave length of the light used (ultra-violet rays). In this connection, in fabricating highly compact IC's, acoustic wave transducers and other devices having a minute pattern of a sub-micron order, a scanning type electron beam pattern generator such as shown in FIG. 1 is used.
In FIG. 1, a beam of electrons from an electron gun 1 passes through a condenser lens 3 and an objective lens 5 so that it is focused on an object 7 in the form of a minute spot. 4 and 4a are aperture diaphragms to limit the converging angle of the beam. A blanking unit 2 is responsive to blanking signals for the on-off controlling of the beam. A beam-deflector unit 6 is responsive to deflecting signals for causing the beam to scan the object and permits the minute spot of the beam to draw a desired pattern thereon. The pattern can be formed by causing the minute spot 8 of the beam to scan the object in such a way that a selected portion 9 is uniformly exposed as shown in FIG. 2.
In actual practice, the scanning type pattern generator is controlled by an associated electronic computer. Specifically, the pattern generator is responsive to blanking and deflecting signals both supplied from the electronic computer for stopping and shifting the electron beam so as to draw a desired pattern on the object. It is required for obtaining an accurate pattern that the beam control system involve complicated compensations for distortion, astigmatism and the shift of the focus each of which varies with the deflection angle of the beam.
With a view to reducing the adverse effect by the aperture aberration of the objective lens on the precision of the pattern to be formed, the converging angle of the beam must be reduced, but this accordingly decreases the beam current, and the pattern exposure time increases by as much. The exposure time can be decreased if a high-sensitivity electron resist is used. In such case there arises a necessity for providing beam on-off and beam deflection and correction controls having high speed response.
An object of this invention is to provide a pattern forming apparatus which permits the formation of a desired pattern on an object at a high speed and with high accuracy, requiring no complicated control.